Motor control system having a reactive power reducing input power system

ABSTRACT

A motor control system powered by an input power source. The system includes a reactive power reducing input power system in electrical communication with a motor and a constant frequency input power source. The reactive power reducing input power system includes an AC-DC converter and a regulator system, wherein the regulator system is in electrical communication with a DC-AC inverter that is in electrical communication with the motor. The system may include an isolation system to electrically isolate the DC-AC inverter from the motor when the DC-AC inverter is not transmitting power to the motor. The system may accept multiple alternating current voltage sources including both single phase and three phase sources.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/771,405, filed on Feb. 20, 2013, which is a continuation of U.S.patent application Ser. No. 12/946,398, filed on Nov. 15, 2010, now U.S.Pat. No. 8,403,112, which is a continuation-in-part of U.S. patentapplication Ser. No. 12/582,445, filed Oct. 20, 2009, now U.S. Pat. No.7,849,971, which is a continuation of U.S. patent application Ser. No.11/267,629, filed Nov. 4, 2005, now U.S. Pat. No. 7,631,730. The entirecontent of each application is incorporated by reference herein.

TECHNICAL FIELD

The instant invention relates to suspended work platform hoist systems,particularly hoist control systems having a high system power factor,acceleration control, and tilt control of a suspended work platform.

BACKGROUND OF THE INVENTION

Suspension type work platforms, also commonly referred to as accessplatforms, are well-known in the art. Such platforms are typicallypowered by a hoist at each end of the platform that raises and lowersthe platform on an associated suspension wire at each end. The hoistsare generally very simple machines including an electric inductionmotor, a gearbox, and a traction mechanism that grips the wire.Generally the electric motors are single-speed motors, however two-speedmotors are available. Traditionally the motors incorporateacross-the-line starters and therefore switch from off to full speed atthe press of a button. The gearboxes reduce the motor speed resulting ina platform velocity generally ranging from 27 feet per minute (fpm) to35 fpm. Therefore, the acceleration of the work platform from standingstill to 27 fpm, or more, occurs essentially instantaneously and isjarring and dangerous, not only to the occupants but also the roofbeams, or anchorage points.

Similarly, traditional systems offer no control over a powereddeceleration of the work platform. This is particularly problematic whentrying to stop the work platform at a particular elevation since theplatform approaches the elevation at full speed and then stopsinstantaneously. This crude level of control offered by traditionalsystems results in repeated starting, stopping, and reversing, or“hunting,” before the desired elevation is obtained. Such repeatedstarts and stops not only prematurely wear the equipment, but aredangerous to the work platform occupants.

Additionally, the hoists used in suspended work platform systems areoften several hundred feet from a power source making voltage dropthrough the conductors a concern that often results in motorsoverheating, premature failure, stalling, and the introduction of boosttransformers. For instance, a typical window washing application mayrequire that a work platform be suspended over five hundred feet fromthe location of the power source, which is typically at the top of thebuilding. Such systems often require boost transformers located at thetop of the building so that the voltage at the location of the hoistremains high enough to facilitate proper operation of the motor(s).

What has been missing in the art has been a system by which the users,employers, equipment manufacturers, or the hoist controls themselves cancontrol the acceleration of the work platform. Further, a system inwhich the velocity can be adjustably limited depending on the particularworking conditions is desired.

SUMMARY OF INVENTION

In its most general configuration, the state of the art is improved witha variety of new capabilities and overcomes many of the shortcomings ofprior devices in new and novel ways. In its most general sense, theshortcomings and limitations of the prior art are overcome in any of anumber of generally effective configurations.

The present suspension work platform hoist system is designed forraising and lowering a suspended work platform. The work platform israised and lowered on one or more wire ropes. The suspension workplatform hoist system includes at least one hoist. More commonly asinistral hoist and a dextral hoist are attached to opposite ends of thework platform. In one embodiment, the hoist has a motor in electricalcommunication with a variable acceleration motor control system. Thevariable acceleration motor control system is releasably attached to thework platform and is in electrical communication with a constantfrequency input power source and the hoist motor.

The variable acceleration motor control system controls the accelerationof the work platform as it is raised and lowered, under power, on theropes by controlling the hoist motor. The suspension work platform hoistsystem also includes a platform control system releasably attached tothe work platform that is in electrical communication with the variableacceleration motor control system and the hoist motor(s). The platformcontrol system may include a user input device designed to acceptinstructions to raise or lower the work platform.

The variable acceleration motor control system not only controls theacceleration of the work platform in the conventional sense of positiveacceleration, but it also controls the negative acceleration, ordeceleration, of the work platform. This provides the ability to slowlyapproach a particular elevation, from above or below, in a controlledfashion so that the elevation is not passed, or overshot.

The variable acceleration motor control system controls the accelerationof the work platform so that it reaches a maximum velocity in no lessthan a predetermined time period. The time period is a minimum of 1second, but is more commonly 2-5 seconds, or more depending on the useof the work platform. In one embodiment the variable acceleration motorcontrol system achieves the acceleration control by converting theconstant frequency input power to a variable frequency power supply.This may be accomplished through the use of a variable frequency drivethat converts the constant frequency input power source to a variablefrequency power supply connected to the hoist motors. The system mayincorporate one variable frequency drive that controls both motors, anindividual variable frequency drive for controlling each motorseparately, or a variable frequency drive for each hoist that cancontrol both motors, as will be disclosed in detail in the DetailedDescription of the Invention.

Further, the suspension work platform hoist system may include a systemdesigned to reduce the reactive power associated with conventionalsuspended hoist systems and produce a hoist system power factor of atleast 0.95 when operating at a steady state full-load condition as themotor raises the work platform. The hoist system power factor takes intoaccount all the power consuming devices of the suspension work platformhoist system as well as a suspended conductor system that connects theconstant frequency input power source to the hoist, which is often inexcess of several hundred feet. A further embodiment achieves a hoistsystem power factor of at least 0.98 when operating at a steady statefull-load condition.

In one embodiment, the hoist system power factor is achieved byincorporating a reactive power reducing input power system into thesuspension work platform hoist system. The reactive power reducing inputpower system includes an AC-DC converter and a regulator system, whereinthe regulator system is in electrical communication with a DC-ACinverter that is in electrical communication with the motor. The DC-ACinverter controls the rate at which the motor accelerates the tractionmechanism thereby controlling the acceleration of the work platform asthe work platform is raised and lowered on the rope. Alternatively, thehoist system (10) may be a constant acceleration hoist systemincorporating a reactive power reducing input power system having acapacitor bank adjacent the motor to achieve the hoist system powerfactor of at least 0.95 in steady state full-load condition.

A further embodiment further including an isolation system thatelectrically isolates the DC-AC inverter from the motor when the DC-ACinverter is not transmitting power to the motor. The isolation systemprevents any current generated by the rotation of the motor during anunpowered descent of the work platform from coming in contact with theDC-AC inverter. Yet a further embodiment includes a descent controlsystem between the isolation system and the motor, wherein in anemergency descent mode the descent control system electromagneticallycontrols the emergency descent of the work platform under the influenceof gravity and limits the emergency descent velocity to 60 feet perminute, and more preferably limits the emergency descent velocity to 45feet per minute or less. If utility power is lost the work platform islocked by a mechanical brake and remains suspended in the air for theoperators' safety. If this happens, the mechanical brake may be releasedmanually to enter the emergency descent mode and to allow the workplatform to descend to the ground at the emergency descent velocity.

The suspension work platform hoist system may further include a tiltcontrol system. The tilt control system is in electrical communicationwith the variable acceleration motor control system and includes atleast one tilt controller and at least one tilt sensor. The tilt controlsystem is capable of detecting the tilt angle of the work platform andcontrolling the variable acceleration motor control system so that thework platform reaches and maintains a tilt angle setpoint as the workplatform is raised and lowered.

Variations of the platform control system may include a GPS trackingsystem as well as a remote wireless transmitter and a receiver. In suchvariations, the remote wireless transmitter transmits commands to thereceiver using spread spectrum communications. Additionally, the remotewireless transmitter may include some, or all, of the controls of theuser input device(s). These variations, modifications, alternatives, andalterations of the various preferred embodiments may be used alone or incombination with one another, as will become more readily apparent tothose with skill in the art with reference to the following detaileddescription of the preferred embodiments and the accompanying figuresand drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Without limiting the scope of the suspension work platform hoist systemas claimed below and referring now to the drawings and figures:

FIG. 1 is a schematic of an embodiment of the suspension work platformhoist system, not to scale;

FIG. 2 is a schematic of an embodiment of the suspension work platformhoist system, not to scale;

FIG. 3 is a schematic of an embodiment of the suspension work platformhoist system, not to scale;

FIG. 4 is a schematic of an embodiment of the suspension work platformhoist system, not to scale;

FIG. 5 is a schematic of an embodiment of the suspension work platformhoist system, not to scale;

FIG. 6 is a schematic of an embodiment of the suspension work platformhoist system, not to scale;

FIG. 7 is a schematic of an embodiment of the suspension work platformhoist system, not to scale;

FIG. 8 is a schematic of an embodiment of the suspension work platformhoist system, not to scale;

FIG. 9 is a schematic of an embodiment of the suspension work platformhoist system, not to scale;

FIG. 10 is a left side elevation view of an embodiment of a hoist of thesuspension work platform hoist system, not to scale;

FIG. 11 is a right side elevation view of an embodiment of a hoist ofthe suspension work platform hoist system, not to scale;

FIG. 12 is a rear elevation view of an embodiment of a hoist of thesuspension work platform hoist system, not to scale;

FIG. 13 is a top plan view of an embodiment of a hoist of the suspensionwork platform hoist system, not to scale;

FIG. 14 is a perspective assembly view of an embodiment of a hoist ofthe suspension work platform hoist system, not to scale;

FIG. 15 is a perspective view of an embodiment of a hoist of thesuspension work platform hoist system, not to scale;

FIG. 16 is a front elevation view of an embodiment of a work platform ofthe suspension work platform hoist system, not to scale;

FIG. 17 is a front elevation view of an embodiment of a work platform ofthe suspension work platform hoist system, not to scale;

FIG. 18 is a schematic of an embodiment of the suspension work platformhoist system, not to scale;

FIG. 19 is a schematic of an embodiment of the suspension work platformhoist system, not to scale;

FIG. 20 is a schematic of an embodiment of the suspension work platformhoist system, not to scale;

FIG. 21 is a schematic of an embodiment of the suspension work platformhoist system, not to scale;

FIG. 22 is a schematic of an embodiment of the suspension work platformhoist system, not to scale;

FIG. 23 is a schematic of an embodiment of the suspension work platformhoist system, not to scale;

FIG. 24 is a schematic of an embodiment of the suspension work platformhoist system, not to scale;

FIG. 25 is a perspective view of an embodiment of the hoist, not toscale;

FIG. 26 is a partial schematic view of an embodiment the suspension workplatform hoist system, not to scale;

FIG. 27 is a partial schematic view of an embodiment the suspension workplatform hoist system, not to scale;

FIG. 28 is a partial schematic view of an embodiment the intelligentcontrol system, not to scale; and

FIG. 29 is a partial schematic view of an embodiment the platformcontrol system, not to scale.

DETAILED DESCRIPTION OF THE INVENTION

The presently disclosed suspension work platform hoist system (10)enables a significant advance in the state of the art. The preferredembodiments of the device accomplish this by new and novel arrangementsof elements and methods that are configured in unique and novel ways andwhich demonstrate previously unavailable but preferred and desirablecapabilities. The detailed description set forth below in connectionwith the drawings is intended merely as a description of the presentlypreferred embodiments of the invention, and is not intended to representthe only form in which the present invention may be constructed orutilized. The description sets forth the designs, functions, means, andmethods of implementing the invention in connection with the illustratedembodiments. It is to be understood, however, that the same orequivalent functions and features may be accomplished by differentembodiments that are also intended to be encompassed within the spiritand scope of the invention.

A suspension work platform hoist system (10) for raising and lowering awork platform (100). In one embodiment, as seen in FIG. 16, the workplatform (100) is raised and lowered on two wire ropes, namely asinistral rope (400) and a dextral rope (500), however the work platform(100) may be raised and lowered on a single rope by a single hoist.Thus, the work platform (100) may be a platform in the traditional senseof a horizontal structure designed for standing upon, however it alsoincludes man lifts, cage lifts, bosun's chairs, and any structuredesigned to support a worker from a suspension rope, while accommodatingchanges in elevation. Generally, the work platform (100) has a sinistralend (110) and a dextral end (120). In one embodiment, the suspensionwork platform hoist system (10) includes a sinistral hoist (200) that isreleasably attached to the work platform (100) near the sinistral end(110) and cooperates with the sinistral rope (400), and a dextral hoist(300) that is releasably attached to the work platform (100) near thedextral end (110) and cooperates with the dextral rope (500). Now,referring to FIGS. 10-15, the sinistral hoist (200) has a sinistralmotor (210) and the dextral hoist (300) has a dextral motor (310), andeach motors (210, 310) is in electrical communication with at least onevariable acceleration motor control system (600). While FIGS. 10-15illustrate only the sinistral hoist (200) and its components, the samefigures apply equally to the dextral hoist (300) since they areidentical, merely substituting 300 series element numbers in place ofthe 200 series element numbers.

With reference now to FIG. 1, the variable acceleration motor controlsystem (600) is releasably attached to the work platform (100) and is inelectrical communication with a constant frequency input power source(800) and the sinistral motor (210) and the dextral motor (310). Thevariable acceleration motor control system (600) controls theacceleration of the work platform (100) as the work platform (100) israised and lowered on the sinistral rope (400) and the dextral rope(500) by controlling the sinistral motor (210) and the dextral motor(310). Lastly, the suspension work platform hoist system (10) mayinclude a platform control system (700) releasably attached to the workplatform (100) and in electrical communication with the variableacceleration motor control system (600), the sinistral motor (210),and/or the dextral motor (300), and has a user input device (710)designed to accept instructions to raise or lower the work platform(100).

In addition to the sinistral motor (210), the sinistral hoist (200) hasa sinistral traction mechanism (220), seen best in FIGS. 11-12, designedto cooperate with the sinistral rope (400), and a sinistral gearbox(230) for transferring power from the sinistral motor (210) to thesinistral traction mechanism (220). Similarly, the dextral hoist (300)has a dextral traction mechanism (320) designed to cooperate with thedextral rope (300), and a dextral gearbox (330) for transferring powerfrom the dextral motor (310) to the dextral traction mechanism (320).The sinistral hoist (220) is releasably attached to the work platform(100) near the sinistral end (110) and the dextral hoist (320) isreleasably attached to the work platform (100) near the dextral end(120). The work platform (100) includes a floor (140) and a railing(130), as seen in FIG. 16.

Referring again to FIG. 1, the variable acceleration motor controlsystem (600) is in electrical communication with the constant frequencyinput power source (800). Such a power source may be any of theconventional alternating current power sources used throughout theworld, including, but not limited to, single phase, as well as threephase, 50 Hz, 60 Hz, and 400 Hz systems operating at 110, 120, 220, 240,380, 480, 575, and 600 volts. The variable acceleration motor controlsystem (600) controls the rate at which the sinistral motor (210)accelerates the sinistral traction mechanism (220) and/or the rate atwhich the dextral motor (310) accelerates the dextral traction mechanism(320) thereby controlling the acceleration of the work platform (100) asthe work platform (100) is raised and lowered on either, or both, thesinistral rope (400) and the dextral rope (500).

The variable acceleration motor control system (600) not only controlsthe acceleration of the work platform (100) in the conventional sense ofpositive acceleration, but it also controls the negative acceleration,or deceleration, of the work platform (100). Such control not onlyeliminates bone jarring starts and stops characteristic of single-speedand two-speed hoists, but also provides the ability to slowly approach aparticular elevation, from above or below, in a controlled fashion sothat the elevation is not passed, or overshot. In fact, in oneembodiment the variable acceleration motor control system (600) includesan approach mode having an adjustable approach velocity setpoint whichlimits the velocity of the work platform (100) to a value of fiftypercent, or less, of the maximum velocity.

The variable acceleration motor control system (600) provides the userthe ability to control the acceleration and set a particular workingvelocity of the work platform (100). For example, if the work platform(100) is being used for window washing then the work platform (100) isbeing advanced relatively short distances at a time, typically 10-12feet, as the work platform (100) is moved from floor to floor. In such asituation there is no need to allow the work platform (100) toaccelerate to the maximum velocity when advancing a floor at a time.Therefore, in one embodiment the variable acceleration motor controlsystem (600) permits the establishment of an adjustable maximum workingvelocity, which is a great safety improvement because advancing fromfloor to floor at a controlled working velocity that is a fraction ofthe maximum velocity reduces the likelihood of accidents.

Such a system still allows the user to command the variable accelerationmotor control system (600) to accelerate to the maximum velocity whentraversing more significant distances. Therefore, the variableacceleration motor control system (600) controls the acceleration of thework platform (100) so that the work platform (100) reaches a maximumvelocity in no less than a predetermined time period to eliminate thebone jarring starts previously discussed as being associated withsingle-speed and two-speed hoist systems. The time period is a minimumof 1 second, but is more commonly 2-5 seconds, or more, depending on theuse of the work platform (100). For instance, greater time periods maybe preferred when the work platform (100) is transporting fluids such aswindow washing fluids or paint.

As previously mentioned, the variable acceleration motor control system(600) is in electrical communication with the constant frequency inputpower (800) and the sinistral motor (210) and/or dextral motor (310), asseen in FIG. 1. In one embodiment, the variable acceleration motorcontrol system (600) achieves the acceleration control by converting theconstant frequency input power to a variable frequency power supply(900) in electrical communication with one, or more, of the motors (210,310), as seen in FIG. 2. In one particular embodiment the variableacceleration motor control system (600) includes a variable frequencydrive (610) that converts the constant frequency input power source(800) to a variable frequency power supply (900) connected to thesinistral motor (210) and the dextral motor (310). As used herein, theterm variable frequency drive (610) means a configuration incorporatingat least an AC-DC converter (640) and a DC-AC inverter (670), as seenschematically in FIG. 26, whether or not they are housed in what somewould refer to as a packaged variable frequency drive, or integratedinto a system containing an AC-DC converter (640) and a DC-AC inverter(670).

The variable frequency drive (610) embodiment may include a furtherembodiment in which a single variable frequency drive (610) is used tocontrol both the sinistral motor (210) and the dextral motor (310). Forexample, a single sinistral variable frequency drive (620) may beincorporated to convert the constant frequency input power source (800)to a sinistral variable frequency power supply (910) in electricalcommunication with the sinistral motor (210) and the dextral motor (310)such that the sinistral motor (210) and the dextral motor (310) arepowered in unison by the sinistral variable frequency power supply(910), as seen in FIG. 4. Alternatively, the variable acceleration motorcontrol system (600) may include a dextral variable frequency drive(630) that converts the constant frequency input power source (800) to adextral variable frequency power supply (920) in electricalcommunication with the sinistral motor (210) and a dextral motor (310)such that the sinistral motor (210) and the dextral motor (310) arepowered in unison by the dextral variable frequency power supply, asseen in FIG. 3. Typically, the single variable frequency drive (610),whether it be the sinistral variable frequency drive (620) or thedextral variable frequency drive (630), is mounted within the body ofeither the sinistral hoist (200) or the dextral hoist (300), with therest of the variable acceleration motor control system (600). Therefore,in this embodiment conductors connected to the constant frequency inputpower source (800) would connect to one of the hoists (200, 300) andpower that particular variable frequency drive (610, 620) that wouldthen provide a variable frequency power supply (910, 920) to both motors(210, 310), one with conductors merely connecting the variable frequencydrive (610, 620) to the motor (210, 310) within the hoist (200, 300) andthe other with conductors traversing the work platform (100) to connectto and power the other hoist (200, 300).

In an alternative variable frequency drive (610) embodiment both thesinistral motor (210) and the dextral motor (310) are associated withtheir own variable frequency drive, namely a sinistral variablefrequency drive (620) and a dextral variable frequency drive (630), asseen in FIGS. 5 and 6. The variable frequency drives (620, 630) may becentrally housed, as seen in FIG. 5, or located at, or in, theindividual hoists (200, 300), as seen in FIG. 6. In one embodiment eachvariable frequency drive (620, 630) powers only the associated motor(210, 310), as seen in FIGS. 5-6. In an alternative embodiment seen inFIGS. 7-9, the sinistral variable frequency drive (620) and a dextralvariable frequency drive (630) are each sized to power both motors (210,310) and never only power a single motor, thereby introducing a fieldconfigurable redundant output power supply capability. Referring firstto the embodiment of FIG. 6 wherein the sinistral variable frequencydrive (620) only powers the sinistral motor (210) and the dextralvariable frequency drive (630) only powers the dextral motor (310), thetwo drives (620, 630) are still a part of the variable accelerationmotor control system (600), regardless of the fact that each drive (620,630) will most likely be housed within the associated hoist (200, 300),and therefore offer all of the previous described control benefits, andeach drive (620, 630) may be controlled in unison with a common controlsignal.

Now, referring back to the embodiment of FIGS. 7-9 wherein each drive(620, 630) is sized to power both motors (210, 310), this embodiment issimilar to the previously described embodiment of FIG. 2 wherein asingle variable frequency drive (610) controls both motors (210, 310),yet the present embodiment introduces redundant capabilities notpreviously seen. In this embodiment the constant frequency input powersource (800) is in electrical communication with both the sinistralvariable frequency drive (620), thereby producing a sinistral variablefrequency power supply (910), and the dextral variable frequency drive(630), thereby producing a dextral variable frequency power supply(920). The sinistral variable frequency power supply (910) is inelectrical communication with the sinistral motor (210) and a dextraloutput power terminal (240). Similarly, the dextral variable frequencypower supply (920) is in electrical communication with the dextral motor(310) and a sinistral output power terminal (340).

Additionally, in this embodiment the sinistral motor (210) is also inelectrical communication with a sinistral auxiliary input power terminal(245) and the dextral motor (310) is also in electrical communicationwith a dextral auxiliary input power terminal (345), as seenschematically in FIG. 7. Therefore, in the configuration of FIG. 8 thevariable acceleration motor control system (600) utilizes the sinistralvariable frequency drive (620) to control both the sinistral and dextralmotors (210, 310), thereby requiring that the dextral output powerterminal (240) be in electrical communication with the dextral auxiliaryinput power terminal (345) via an auxiliary conductor (950). In thealternative configuration of FIG. 9 the variable acceleration motorcontrol system (600) utilizes the dextral variable frequency drive (620)to control both the sinistral and dextral motors (210, 310), therebyrequiring that the sinistral output power terminal (340) be inelectrical communication with the sinistral auxiliary input powerterminal (245) via an auxiliary conductor (950). The auxiliary conductor(950) may be a set of loose conductors or the conductors may bepermanently attached to the work platform (100). These embodimentsprovide the hoist system (10) with a field configurable redundant outputpower supply capable of controlling the acceleration of the workplatform (100) upon failure of either the sinistral variable frequencydrive (620) or the dextral variable frequency drive (630).

A further variation of the above embodiment incorporates an alternatorthat ensures that each time the work platform (100) starts, the oppositevariable frequency drive (620, 630) supplies the variable frequencypower supply to both motors (210, 310). Alternatively, the alternatormay cycle the variable frequency drives (620, 630) based upon the amountof operating time of the drives (620, 630). These embodiments ensuresubstantially equal wear and tear on the variable frequency drives (620,630). Still further, the system (10) may incorporate an automaticchangeover features so that if one variable frequency drive (620, 630)fails then the other variable frequency drive (620, 630) automaticallytakes over. As an additional safety measure, the variable frequencydrives (610, 620, 630) may incorporate a bypass switch allowing theconstant frequency input power source to be directly supplied to thesinistral motor (210) and the dextral motor (310), thereby permittingthe variable frequency drives (610, 620, 630) to serve asacross-the-line motor starters.

Another embodiment incorporates an enclosure, or enclosures, for thehoist components thereby improving the operating safety, equipment life,serviceability, and overall ruggedness. For instance, in one embodiment,seen in FIG. 15, the sinistral motor (210), the sinistral tractionmechanism (220), and the sinistral gearbox (230), seen in FIG. 14, aretotally enclosed in a sinistral housing (250) attached to a sinistralchassis (260). Similarly, the dextral motor (310), the dextral tractionmechanism (320), and the dextral gearbox (330) may be totally enclosedin a dextral housing (350) attached to a dextral chassis (360). Further,with reference now to FIG. 14, the sinistral chassis (260) may include asinistral handle (262) and at least one rotably mounted sinistral roller(264) configured such that the sinistral hoist (200) pivots about thesinistral roller (264) when the sinistral handle (262) is acted upon, sothat the sinistral hoist (200) may be easily transported via rollingmotion. Similarly, the dextral chassis (360) may include a dextralhandle (362) and at least one rotably mounted dextral roller (364)configured such that the dextral hoist (300) pivots about the dextralroller (364) when the dextral handle (362) is acted upon, so that thedextral hoist (300) may be easily transported via rolling motion.Further, it is often desirable to have very compact hoists (200, 300) sothat they may fit through small opening in confined spaces to carry outwork. One such occasion is when performing work on the inside of anindustrial boiler wherein the access hatches are generally eighteeninches in diameter. Therefore, in one embodiment, seen in FIGS. 14-15,the sinistral hoist (200), sinistral housing (250), and sinistralchassis (260) are configured to pass through an eighteen inch diameteropening and the dextral hoist (300), dextral housing (350), and dextralchassis (360) are configured to pass through an eighteen inch diameteropening, while having a weight of less than 120 pounds.

As previously mentioned, the variable acceleration motor control system(600) is releasably attached to the moving work platform (100). In theembodiments incorporating variable frequency drives (610, 620, 630) andhoist housings (250, 350), the variable frequency drives (610, 620, 630)are most commonly mounted within one, or more, of the hoist housings(250, 350). In fact, in a preferred embodiment the sinistral hoist (200)has its own sinistral variable frequency drive (620) housed within thesinistral hoist housing (250), and similarly the dextral hoist (300) hasits own dextral variable frequency drive (630) housed within the dextralhoist housing (350). In such an embodiment, seen in FIG. 15, it is alsoideal to have the dextral power terminal (240) as a dextralweather-tight conductor connector (242) located on the sinistral hoist(200), and the sinistral power terminal (340) as a sinistralweather-tight conductor connector (342) located on the dextral hoist(300). The weather-tight conductor connectors (242, 342) and powerterminals (240, 340) may be any number of male, or female, industrialplugs and receptacles that cooperate with conductors sized to handle theelectrical load of supplying power to either of the motors (210, 310).

In yet another embodiment, the variable acceleration motor controlsystem (600) monitors the constant frequency input power source andblocks electrical communication to the sinistral motor (210) and thedextral motor (310) when the voltage of the constant frequency inputpower source varies from a predetermined voltage by more than plus, orminus, at least ten percent of the predetermined voltage. Further, thevariable acceleration motor control system (600) may incorporatereporting devices to signal to an operator the reason that the system(600) has been shut down. The variable acceleration motor control system(600) may also monitor the load on the sinistral traction mechanism(220) and the dextral traction mechanism (320) and blocks electricalcommunication to the sinistral motor (210) and the dextral motor (310)if (a) either the sinistral traction mechanism (220) loses traction onthe sinistral rope (400) or the dextral traction mechanism (320) losestraction on the dextral rope (500), (b) the load on the work platform(100) exceeds a predetermined value, or (c) the load on the workplatform (100) is less than a predetermined value.

The platform control system (700) and the user input device (710) mayincorporate functions other than merely accepting instructions to raiseor lower the work platform (100). Generally the industry refers to theplatform control system (700) as a central control box, which mayinclude numerous buttons and switches, or user input devices (710), forcontrolling the suspension work platform hoist system (10). In oneparticular embodiment the platform control system (700) includes apendant so that the operator does not need to be located at the userinput device (710) to control the movement of the work platform (100).In other words, the user input device (710) may be at least one controlswitch, button, or toggle located on a fixed central control box, or itmay be all, or some, of those same devices located on a movable pendent.Generally, the user input device (710) will include up/down hold-to-runswitches, hoist selector switches (sinistral, dextral, both), and anemergency stop button. Various embodiments of the present invention maycall for the addition of input devices associated with the variableacceleration motor control system (600). Such additional input devicesmay include (a) approach mode enable/disable, (b) adjustable approachvelocity setpoint, (c) work mode enable/disable, (d) adjustable approachvelocity setpoint, (e) adjustable acceleration period setpoint, and (f)hoist master/slave selector to identify which hoist generates thecontrol power or control signal and which merely receives the power orcontrol signal and responds accordingly. The platform control system(700) and/or the user input device (720) may incorporate a LCD screen toview diagnostics and setpoints. Further, the LCD screen may be atouch-screen input system.

Even further, the platform control system (700) may incorporate adiagnostic system (750), as seen in FIG. 1, that allows the user toperform specific tests of the system (10) and makes the user aware ofcertain conditions, and that performs a predetermined set of testsautomatically. The diagnostic system (750) permits the user to initiatesystem tests, or checks, including testing the panel light integrity aswell as the level of the input voltage. Further, the diagnostic system(750) may run automatic system tests including (a) ultra-high top limitdetection, (b) tilt sensing in up to 4 axes, (c) ultra-bottom limitdetection, (d) under load detection, (e) overload detection, (f) fallprotection interlock integrity, or Sky Lock interlock integrity, (g)motor temperature, (h) brake voltage level, (i) rope jam sensing, (j)wire-winders integrity, (k) main voltage phase loss integrity, (l)end-of-rope sensing integrity, (m) digital speed read-out, (n) digitalfault display, (o) rope diameter sensing integrity, and/or (p) platformheight protector integrity. In other words, the diagnostic system (750)may run automatic tests to ensure that every safety feature isoperational and properly functioning. The diagnostic system (750)automatic tests may be programmed to run every time the hoist isoperated, or on an alternative schedule. The diagnostic system (750) mayinclude any number of visual indicators (752), seen in FIG. 14, to alertthe user of particular conditions. For instance, each of the abovelisted automatic tests may have a unique visual indicator (752) toinform the user whether the test was a success, or failure. The visualindicators (752) may be light emitting diodes, or LED's, LCD displaysuch as 2×16, 2×20, or 2×40, or similar type readouts.

Another advantage of the present platform control system (700) is thatit incorporates a printed circuit board (PCB), thereby offeringfunctionality and flexibility not previously seen in hoist system. ThePCB facilitates the easy incorporation of numerous optional features bysimply plugging them into the appropriate ports on the PCB allowing anunprecedented degree of modularity. The control system software includesplug-and-play type features that automatically recognize new componentsplugged into the PCB. The substrate of the PCB is an insulating andnon-flexible material. The thin wires are visible on the surface of theboard are part of a copper foil that initially covered the whole board.In the manufacturing process the copper foil is partly etched away, andthe remaining copper forms a network of thin wires. These wires arereferred to as the conductor pattern and provide the electricalconnections between the components mounted on the PCB. To fasten themodular components to the PCB the legs on the modular components aregenerally are soldered to the conductor pattern or mounted on the boardwith the use of a socket. The socket is soldered to the board while thecomponent can be inserted and taken out of the socket without the use ofsolder. In one embodiment the socket is a ZIF (Zero Insertion Force)socket, thereby allowing the component to be inserted easily in place,and be removable. A lever on the side of the socket is used to fastenthe component after it is inserted. If the optional feature to beincorporated requires its own PCB, it may connect to the main PCB usingan edge connector. The edge connector consists of small uncovered padsof copper located along one side of the PCB. These copper pads areactually part of the conductor pattern on the PCB. The edge connector onone PCB is inserted into a matching connector (often referred to as aSlot) on the other PCB. The modular components mentioned in thisparagraph may include a GPS tracking device (720) and a wirelessreceiver (740), just to name a few.

The platform control system (700) may further include a GPS trackingdevice (720), shown schematically in FIG. 1. The GPS tracking device(720) allows the owner of the suspension work platform hoist system (10)to track its location real-time. The GPS tracking device (720) may be abattery powered 12, or more, channel GPS system capable of up to 120days of operation based upon 10 reports a day, powered by 6 AA alkalinebatteries or 6-40 VDC. The GPS tracking device (720) has an internalantenna and memory to record transmissions when cellular service is pooror lost. The GPS tracking device (720) may be motion activated. The GPStracking device (720) may be manufactured by UTrak, Inc., a MiniatureCovert GPS Tracking System Item#: SVGPS100, a RigTracker trackingsystem, or a Laipac Technology, Inc. tracking system, just to name afew.

Further, still referring to FIG. 1, the platform control system (700)may include a remote wireless transmitter (730) and a receiver (740)wherein the remote wireless transmitter (730) transmits commands to thereceiver (740) using spread spectrum communications. The remote wirelesstransmitter (730) may include some, or all, of the controls of the userinput device(s) (710) discussed herein. The spread spectrumcommunications may utilize digital frequency hopping or analogcontinuous frequency variation, generally on 900 MHz to 2.4 GHz carrierfrequencies. Additionally, the remote wireless transmitter (730) iscapable of transmitting commands to the receiver (740) with a range ofat least one thousand feet, and up to three thousand feet. Spreadspectrum communications are less susceptible to interference,interception, exploitation, and spoofing than conventional wirelesssignals. This is important due to the safety concerns associated withcontrolling a suspended work platform (100) from a remote location. Thespread spectrum communication system varies the frequency of thetransmitted signal over a large segment of the electromagnetic radiationspectrum, often referred to as noise-like signals. The frequencyvariation may be accomplished according to a specific, but complicated,mathematical function often referred to as spreading codes,pseudo-random codes, or pseudo-noise codes. The transmitted frequencychanges abruptly many times each second. The spread spectrum signalstransmit at a much lower spectral power density (Watts per Hertz) thannarrowband transmitters.

In yet another embodiment, the suspension work platform hoist system(10) includes elements to reduce the reactive power associated withconventional suspended hoist systems and produce a hoist system powerfactor of at least 0.95 when operating at a steady state full-loadcondition as the motor (210) raises the work platform (100) on the rope(400). The hoist system power factor takes into account all the powerconsuming devices of the suspension work platform hoist system (10) aswell as a suspended conductor system (810) that connects the constantfrequency input power source (800) to the hoist (200), which is often inexcess of several hundred feet. A further embodiment achieves a hoistsystem power factor of at least 0.98 when operating at a steady statefull-load condition.

In one embodiment, the hoist system power factor is achieved byincorporating a reactive power reducing input power system (1300) intothe suspension work platform hoist system (10). As seen schematically inFIG. 26, in one embodiment the reactive power reducing input powersystem (1300) includes an AC-DC converter (640) and a regulator system(650), wherein the regulator system (650) is in electrical communicationwith a DC-AC inverter (670) that is in electrical communication with themotor (210). The DC-AC inverter (670) controls the rate at which themotor (210) accelerates the traction mechanism (220) thereby controllingthe acceleration of the work platform (100) as the work platform (100)is raised and lowered on the rope (400).

In yet another embodiment, the reactive power reducing input powersystem (1300) accepts input voltages from single phase 200 VAC to threephase 480 VAC, and the regulator system (650) includes a buck regulatortopology generating direct current voltage supply of less than 330 VDCto the DC-AC inverter (670). An even further embodiment incorporates atoroidal stack having an inductance of at least 2 millihenry in the buckregulator topology. The toroidal stack provides a stabilized inductanceat a fairly high current, over a wide range of voltages. Alternatively,the reactive power reducing input power system (1300) may accept asingle phase voltage, and the regulator system (650) may include a boostregulator topology generating direct current voltage supply of less than330 VDC to the DC-AC inverter (670), wherein the boost regulator has aninductance of at least 3 millihenry. In this single phase embodiment,the high hoist system power factor, combined with the boost regulatortopology, produces an adequate power supply to the DC-AC inverter (670)for operation of the motor (210) even when input power to the reactivepower reducing input power system (1300) is between 85 VAC and 95 VAC,thereby eliminating the need for external boost transformers that areoften required in suspended work platform applications due to largereactive power requirements associated with the induction machines thatare used as hoist motors, and the excessive voltage drops common insuspended work platform applications where it is common for thesuspended conductor system (810) to extend a great distance between theconstant frequency input power source (800) and the hoist (200).

In one embodiment the reactive power reducing input power system (1300)utilizes a single active switch and a control algorithm that senses therectified input voltage to facilitate the regulator system (650) drawingcurrent such that the current and voltage from the constant frequencyinput power source (800) are substantially in phase, resulting in thehigh hoist system power factor. Further, in this embodiment theregulator system (650) is configured to facilitate a fail safe mode suchthat if the DC-AC inverter (670) fails the resulting circuit is simply a3-phase rectifier and an LC filter. Further, utilizing a single activeswitch is significantly less costly than traditional methods such as sixactive switch PFC input or a Vienna Rectifier approach.

Utilization of a regulator system (650) incorporating a boost regulatortopology, or buck regulator topology, to generate direct current voltagesupply of less than 330 VDC to the DC-AC inverter (670), in conjunctionwith a standard three phase rectifier to achieve power factorcorrection, enables the electronic load to appear as a resistor to theconstant frequency input power source (800). This is particularlyimportant as the kVA rating of motor (210) goes up. Regardless oftopology, the following fundamental relationships remain true. Apparentpower is a complex vector. Average power is the real component, andreactive power is the complex component of this vector.S=P+j×QS is the apparent power in VA, P is the average power in Watts, and Q isthe reactive power in VARS. Power factor is defined as:

${P\; F} = \frac{P}{S}$The above equation holds true for instants in time, where P and S mayhave numerous harmonics integrated into them. If one considers anotherdefinition of power:P=V×I×cos(θ)The above is the real power as a function of V, I, and the fundamentaldisplacement power factor, i.e. the power factor associate with thefundamental frequency of V and I. A more complete way to look at powerfactor is:PF=HF×DFwhich says that power factor is the product of the Harmonic Factor andthe Displacement Power Factor. Finally, Harmonic Factor is determinedby:

${H\; F} = \frac{1}{\left( {1 + {THD}^{2}} \right)}$In order to ascertain the performance advantage to a building'selectrical system, and consequently the electrical power grid,mathematical analysis is undertaken to quantitatively indicate theperformance advantage (i.e. reduced transmission line losses and reducedpower generation required at the source). Consider the inductionmachine, with the Thevenin impedance at the terminals given by:Z _(machine) =R+jωLThe real power absorbed by the machine is:P _(machine)=(I _(machine))² ×RThe real power absorbed by the machine is:Q _(machine)=(I _(machine))² ×ω×LAn optimal case for the building electrical power system occurs when theterm of Qmachine approaches 0, because the apparent power (S) is reducedto solely active power (P) and the currents supplied to the inductionmachine will be minimum.

A reasonable power factor for a lower power induction machine is on theorder of 0.7 to 0.8. Using a power factor of 0.7, one can determine howmuch reactive power is consumed for a 3.0 HP induction machine, inconjunction with the typical acceptable value for converting between HPand Watts. Consider, for example.

$P_{machine} = {{0.746 \times \frac{Watts}{HP} \times 3.0\mspace{14mu}{HP}} = {2.238\mspace{14mu}{KW}}}$Now calculating how much reactive power the machine would draw:

$S_{machine} = {\frac{P_{machine}}{P\; F} = {\frac{2238}{.7} = {3.2\mspace{14mu}{kVA}}}}$Now consider how much current would be needed by the machine in the caseof the 0.8 lagging power factor:

$I_{building} = {\frac{S_{{lagging}_{pf}}}{V_{rms} \times \sqrt{3}} = {\frac{3.2\mspace{14mu}{kVA}}{230\mspace{14mu} V \times 1.732} = {8.03\mspace{14mu}{Amps}}}}$Now consider how much current would be needed by the machine in the caseof a unity power factor case:

$I_{{building}^{*}} = {\frac{S_{{unity}_{pf}}}{V_{rms} \times \sqrt{3}} = {\frac{2.24\mspace{14mu}{kW}}{230\mspace{14mu} V \times 1.732} = {5.62\mspace{14mu}{Amps}}}}$Now, consider a suspended hoist application utilizing a suspendedconductor system (810) of 12 AWG, having a resistance of:

$R_{{cable}_{12\;{AWG}}} = \frac{1.588\;\Omega}{1,000\mspace{14mu}{feet}}$Now, assuming that the length of the current path in the suspendedconductor system (810) is 1000 feet, the total resistance is 1.588. Nowcalculating the transmission line power losses for the 0.8 lagging powerfactor example:P _(cable)(8.03 Amps)²×1.588Ω=102.4WThe transmission line power losses for the unity power factor example:P _(cable)=(5.62 Amps)²×1.588Ω=50.15WThus the power losses are more than double in the case of a non-unitypower factor corrected system. Further, the power losses in thetransmission line at non-unity power factor are non-trivial; after all,100 Watts of power loss contributes to voltage drop at the motorterminals. Consider the voltage drop:V _(drop)=8.03 Amps×1.588Ω=12.75VThus, the reactive power reducing input power system (1300) producespower factor correction resulting in reduced voltage drop at the motorterminals, reduced transmission line power losses which will ofteneliminate the need for an external boost transformer in suspended workplatform applications, reduced power generation requirement of thebuilding electrical system, and reduced power generation requirement ofthe grid supplying the building electrical system.

Now, referring back to the embodiment in which the reactive powerreducing input power system (1300) accepts input voltages from singlephase 200 VAC to three phase 480 VAC; one further specific embodimentincorporates the regulator system (650) in a buck regulator topologygenerating direct current voltage supply of less than 330 VDC to theDC-AC inverter (670) such that the constant frequency input power source(800) may be single phase 230 VAC, or three phase 230 VAC, 380 VAC, or480 VAC. Controlling the DC voltage to the DC-AC inverter (670) to 330VDC or less facilitates the use of an inverter (670) having a rating of600 V or less, instead of 1200 V rated IGBT's that are common ininverters. Yet another embodiment utilizes a reactive power reducinginput power system (1300) with the regulator system (650) in a buckregulator topology generating direct current voltage supply of less than300 VDC to the DC-AC inverter (670); while yet a further embodimentgenerates a direct current voltage supply of less than 275 VDC to theDC-AC inverter (670).

The unique configuration of the reactive power reducing input powersystem (1300) and DC-AC inverter (670) facilitates such a wide range ofacceptable input power supplies that one embodiment of the hoist (200)incorporates a multiple input power connection system (1400) includingat least one single phase power connector (1410) and at least one threephase power connector (1420), as seen in FIG. 25. Such a configurationallows a user to simply connect the appropriate power connector (1410,1420) to correspond to the job site, while utilizing the same hoist(200). This feature is particularly beneficial to equipment rentalbusinesses that rent hoists to contractors. For example, the equipmentrental business would now have one hoist (200) that works with at leastfour different input power situations (single phase 230 VAC, or threephase 230 VAC, 380 VAC, or 480 VAC) simply by connecting an appropriatesingle phase power connector (1410) or three phase power connector(1420); eliminating the need to stock a specific hoist for eachanticipated power situation, which results in wasted space, inventory,and a lot of idle time.

In one embodiment the location and packaging of the reactive powerreducing input power system (1300) and the DC-AC inverter (670) arewithin the hoist (200), meaning within the housing illustrated in FIG.25. In this embodiment the reactive power reducing input power system(1300) and the DC-AC inverter (670) occupy a volume in cubic inches thatis less than three times the weight of the hoist (200) in pounds. Thisrelationship balances the effect that generally lightweight but highvolume consuming electronics have on the center of gravity of the hoist(200) which has a much higher density, as well as the overall size ofthe hoist (200). For example, in one embodiment the total weight of thehoist (200), seen in FIGS. 14-15, is less than 110 pounds, and the totalvolume occupied by the reactive power reducing input power system (1300)and the DC-AC inverter (670) is less than 330 cubic inches. In a furtherembodiment, the reactive power reducing input power system (1300) andthe DC-AC inverter (670) are housed in separate compartments within thehoist (200) to better allocate these lightweight regions. In fact, inthis embodiment the reactive power reducing input power system (1300)occupies a volume in cubic inches that is less than 1.5 times the weightof the hoist (200) in pounds, and the DC-AC inverter (670) occupies asecond volume in cubic inches that is less than 1.3 times the weight ofthe hoist (200) in pounds.

Referring again to FIGS. 26-27, another embodiment further including anisolation system (680) that electrically isolates the DC-AC inverter(270) from the motor (210) when the DC-AC inverter (270) is nottransmitting power to the motor (210). The isolation system (680)prevents any current generated by the rotation of the motor (210) duringan unpowered descent of the work platform from coming in contact withthe DC-AC inverter (270).

Yet a further embodiment includes a descent control system (690) betweenthe isolation system (680) and the motor (210), wherein in an emergencydescent mode the descent control system (690) electromagneticallycontrols the emergency descent of the work platform (100) under theinfluence of gravity and limits the emergency descent velocity to 60feet per minute, and more preferably limits the emergency descentvelocity to 45 feet per minute or less. If utility power is lost thework platform (100) is locked by a mechanical brake and remainssuspended in the air for the operators' safety. If this happens, themechanical brake may be released manually to enter the emergency descentmode and to allow the work platform (100) to descend to the ground atthe emergency descent velocity.

In this embodiment, when the platform descends, the DC-AC inverter (270)is isolated from the induction machine by the isolation system (680),seen in FIGS. 26 and 27, and the machine works as an independent systemhaving a generator with capacitors. The motor (210) generates an ACvoltage across its terminals because of the interaction between therotation of the rotor and the residual magnetism. In a furtherembodiment, the descent control system (690) creates a descent circuitconnected to two terminals of the motor (210) and contains at least onedescent capacitor thereby allowing the motor (210) to function as agenerator creating a descent voltage of 100 VAC to 400 VAC across the atleast one descent capacitor. The at least one descent capacitor helps toconduct the current flow through the rotor coils such that the rotor cankeep rotating as the normal operation because of the electromagnetictorque. In an even further embodiment, the descent control system (690)electromagnetically controls the emergency descent of the work platform(100) under the influence of gravity and limits the emergency descentvelocity to 35 feet per minute. The isolation system (680) alsoseparates the at least one descent capacitor from the reactive powerreducing input power system (1300) and the DC-AC inverter (270), therebyeliminating those components from influencing the impedance in thedescent circuit.

As previously mentioned, the suspension work platform hoist system (10)may include a platform control system (700), which is often referred toin the industry as a central control box (CCB). In one such embodimentthe suspension work platform hoist system (10) may include one reactivepower reducing input power system (1300) supplying power to multipleDC-AC inverters (270), which may include a dedicated DC-AC inverter(270) for each hoist (200, 300), and optionally may include auxiliarywire winders, trolleys, etc. In essence, powering the major powerconsuming devices from one common DC bus further introduces the benefitof a near unity power factor for substantially all of the electricalload associated with the operation of the suspension work platform hoistsystem (10) and related auxiliaries. Obviously, the electrical load inthis case would be increased due to the auxiliaries such as wirewinders, trolleys, etc. and therefore the benefits of a near unity powerfactor would take on added significance. In fact, in one such embodimentthe common reactive power reducing input power system (1300) supplies aload of at least 5 kW with the hoist system power factor of at least0.95, versus supplying a 2-3 kW load as would be the case with two orthree hoists, as is common in many suspended work platform situations.Additionally, the use of one reactive power reducing input power system(1300) to supply power to multiple DC-AC inverters (270) increasesreliability and reduces costs for the overall system, and enablesgreater control of the hoists by having the controls located in a commoncentral location. Further, diagnostic and prognostic functions areenhanced and allow immediate discernment by the operator as to whether afaulted or dangerous condition with the hoist exists.

In yet another embodiment, the hoist system (10) is a constantacceleration hoist system and the reactive power reducing input powersystem (1300) includes a capacitor bank adjacent the motor (210) toachieve the hoist system power factor of at least 0.95 in steady statefull-load condition as the motor (210) raises the work platform (100) onthe rope (400). The following example is an illustration of thiscapacitor bank embodiment. For convenience, this analysis assumes theuse of a 1-hp motor. Many applications using a low-horsepower electricmotor will be fed by a #12-gauge cable and protected at a load center(main panel), the constant frequency input power source (800), by a 20-Acircuit breaker. For this analysis, the suspended conductor system (810)includes an average two-conductor cable length from the load center tothe hoist (200) containing the electric motor (210) that is at least 50feet from the main panel to the hoist (200), for a total length of 100feet, significantly less than the average suspended work platformapplication. Additionally, this example assumes, for the purposes ofillustration only, that the motor (210) is a 1-hp motor with a 85%efficiency and a lagging power factor of 0.75.

Power-factor analysis of the power delivered to a single-phase, 1-hpelectric motor (210) fed by a 120-V electric circuit requires aknowledge of motor (210) and cable, suspended conductor system (810),characteristics. In this particular example, the suspended conductorsystem (810) is assumed to be a 50 foot long section of #12-gauge Romexcable.

The first task is to determine the resistance of 100 feet of cable(resistance of both the hot and neutral wires). The resistance of#12-gauge wire is 1.588Ω/1,000 feet, so Rcable=1.588 Ω/1,000 ft×100feet=0.1588Ω.

The electrical equivalent of an electric motor can be symbolized as aninductive reactance in series with a resistance. The inductive reactanceis due to the stator inductance and reflected inductance of the rotor.The resistance is caused by wire resistance (both stator and reflectedresistance of the rotor) combined with losses due to hysteresis and eddycurrents, mechanical resistances such as bearing losses, and windage.

The power factor is defined as the real power divided by the apparentpower of a system. In this case, assuming a motor has an internalresistance of 8Ω and an inductive reactance of j6. The total impedanceof the motor would be:Z _(MOTOR) =8+j6=10∠36.86989°The real power of the motor is determined by the square of the amperagetimes the motor's internal resistance.RP_(MOTOR) =I ² ×R _(MOTOR)The apparent power of the motor is determined by the square of theamperage time the motor's total impedance.AP_(MOTOR) =I ²× Z _(MOTOR)Therefore:

$\begin{matrix}{{P\; F_{MOTOR}} = \frac{{RP}_{MOTOR}}{{AP}_{MOTOR}}} \\{= \frac{I^{2} \times R_{MOTOR}}{I^{2} \times \overset{\_}{Z_{MOTOR}}}} \\{= \frac{R_{MOTOR}}{\overset{\_}{Z_{MOTOR}}}} \\{= \frac{8\;\Omega}{10{\angle 36}{.86989}{^\circ}\mspace{11mu}\Omega}}\end{matrix}$PF_(MOTOR)=0.8Then:

R_(TOTAL) = .1588 Ω_(CABLE) + 8 Ω_(MOTOR) = 8.1588 Ω $\begin{matrix}{\overset{\_}{Z_{TOTAL}} = {\overset{\_}{Z_{CABLE}} + \overset{\_}{Z_{MOTOR}}}} \\{= {0.1588 + {j\; 0} + 8 + {j\; 6}}} \\{= {10.127{\angle 36}{.33}{^\circ}\mspace{14mu}\Omega}}\end{matrix}$ $\begin{matrix}{{P\; F_{SYSTEM}} = \frac{{RP}_{TOTAL}}{{AP}_{TOTAL}}} \\{= \frac{I^{2} \times R_{TOTAL}}{I^{2} \times \overset{\_}{Z_{TOTAL}}}} \\{= \frac{R_{TOTAL}}{\overset{\_}{Z_{TOTAL}}}} \\{= \frac{8.1588\;\Omega}{10.127{\angle 36}{.33}{^\circ}\mspace{14mu}\Omega}}\end{matrix}$ P F_(SYSTEM) = 0.8056Due to cable resistance, the full 120 V is not applied to the motor,rather by the voltage divider rule:

$\begin{matrix}{\overset{\_}{V_{MOTOR}} = {\overset{\_}{V_{SOURCE}} \times \frac{\overset{\_}{Z_{MOTOR}}}{\overset{\_}{Z_{TOTAL}}}}} \\{= {120{\angle 0{^\circ}} \times \frac{8 + {j\; 6}}{0.1588 + 8 + {j\; 6}}}} \\{= {118.489{\angle 0}{.54}{^\circ}}}\end{matrix}$The power delivered to the system is:P _(IN SYSTEM) =|Ē|×|Ī|×cos θ=120×11.8945×cos(36.33°)=1145.52WThe power delivered to the motor is:P _(IN MOTOR)=| V _(MOTOR) |×|Ī|×cosθ=118.489×11.8495×cos(36.86989°)=1123.23WAssuming a 75% motor efficiency:

P_(OUT) = P_(IN) × Efficiency = 1123.23 × 0.75 = 842.42  W${P_{OUT}({hp})} = {{{P_{OUT}({watts})} \times \frac{1\mspace{14mu}{hp}}{746.7\mspace{14mu} W}} = {\frac{842.42}{746.7} = {1.128\mspace{14mu}{hp}}}}$Now, introducing the reactive power reducing input power system (1300)does not affect the power factor of the motor, rather it only correctsthe power factor that the cable plus load presents to the constantfrequency input power source (800). Thus, performing the abovecomputations but with the system load only represented by a resistance:Z _(MOTOR) =8+j6=10∠36.86989°Then, selecting a capacitor bank having a capacitive reactance equal to16.6667Ω,Z _(TOTAL) = Z _(CABLE) + Z _(MOTOR)=0.1588+j0+12.5+j0=12.6588+j0=12.6588∠0°Calculating the value of the electrical current feeding the suspendedconductor system (810) yields:

$I_{TOTAL} = {\frac{\overset{\_}{E}}{\overset{\_}{Z_{TOTAL}}} = {\frac{120{\angle 0{^\circ}}}{12.6588{\angle 0{^\circ}}} = {9.47957{\angle 0{^\circ}}}}}$Now, assuming for the present example that the reactive power reducinginput power system (1300) produces a system power factor of unity, thePF_(SYSTEM)=1.0. Due to the cable resistance, the full 120 V would notbe applied to the motor. By the voltage divider rule:

$\begin{matrix}{\overset{\_}{V_{MOTOR}} = {\overset{\_}{V_{SOURCE}} \times \frac{\overset{\_}{Z_{MOTOR}}}{\overset{\_}{Z_{TOTAL}}}}} \\{= {120{\angle 0{^\circ}} \times \frac{12.5{\angle 0{^\circ}}}{0.1588 + 12.5}}} \\{= {118.495{\angle 0{^\circ}}}}\end{matrix}$The power delivered to the system is:P _(IN SYSTEM) =|Ē|×|Ī|×cos θ=120×9.47957×cos(0°)=1137.55WThe power delivered to the motor is:P _(IN MOTOR)=| V _(MOTOR) |×|Ī|×cos θ=118.489×9.47957×cos(0°)=1123.28WAssuming a 75% motor efficiency:

P_(OUT) = P_(IN) × Efficiency = 1123.28 × 0.75 = 842.46  W${P_{OUT}({hp})} = {{{P_{OUT}({watts})} \times \frac{1\mspace{14mu}{hp}}{746.7\mspace{14mu} W}} = {\frac{842.46}{746.7} = {1.128\mspace{14mu}{hp}}}}$The reactive power reducing input power system (1300) only affects thetransmission-line losses (the PF of the motor is an inherentcharacteristic of the motor), so the power savings due to theintroduction of the reactive power reducing input power system (1300)can be determined. In this example, without the reactive power reducinginput power system (1300), P=I²R_(CABLE)=(11.85)²×0.1588=22.3 W, whereasafter the introduction of the reactive power reducing input power system(1300) the power loss associated with the suspended conductor system(810) is P=I²R_(CABLE)=(9.48)²×0.1588=14.7 W, which is a 34% reductionin power dissipated in the suspended conductor system (810), and thissimplified example utilized a much shorter current path than the averagesuspended work platform application. Thus, in one embodiment thereactive power reducing input power system (1300) produces a system inwhich the power loss in the suspended conductor system (810) is lessthan 0.3 W per linear foot of length of the suspended conductor system(810) from the constant frequency input power source (800).

The constant acceleration hoist system embodiment described above havingthe reactive power reducing input power system (1300) that includes acapacitor bank adjacent the motor (210), may also include a descentcontrol system (690), as previously described above, wherein in anemergency descent mode the descent control system (690)electromagnetically controls the emergency descent of the work platform(100) under the influence of gravity and limits the emergency descentvelocity to 60 feet per minute. Still further, the descent controlsystem (690) may create a descent circuit connected to two terminals ofthe motor (210) and contains at least one descent capacitor therebyallowing the motor (210) to function as a generator creating a descentvoltage of 100 VAC to 400 VAC across the at least one descent capacitor.The configuration of FIG. 27 illustrates two descent capacitors. Evenfurther, the descent control system (690) may electromagneticallycontrol the emergency descent of the work platform (100) under theinfluence of gravity and limit the emergency descent velocity to 35 feetper minute. The basic theory is that the residual magnetic field on therotor structure of the induction machine, i.e. motor (210), resonateswith the at least one descent capacitor and the induction machinetransitions to generator mode as an external mechanical prime mover,namely the gravitational weight of the suspended work platform (100)translated to a torque on the shaft of the motor (210), actuates therotor.

One particular embodiment incorporates a descent capacitor having acapacitance of at least 60 μF to maintain the voltage generated in thedescent circuit at less than 400 VAC and a current of less than 20 Amps,while controlling the descent of a 1200 pound load at less than 45 feetper minute. In yet another embodiment, a descent capacitor having acapacitance of at least 150 μF is incorporated to maintain the voltagegenerated in the descent circuit at less than 300 VAC and a current ofless than 10 Amps, while controlling the descent of a 1200 pound load atless than 35 feet per minute. A further embodiment has recognized aunique relationship among variables necessary to provide a descentcircuit with the desired control over a 1200 pound load; namely, thedescent circuit should have at least one descent capacitor with acapacitance in μF of at least 2.5 times the desired descent velocity infeet per minute. Yet another embodiment recognizes another uniquerelationship among variables necessary to provide a descent circuit withthe desired control over a 1200 pound load; namely, the descent circuitshould have at least one descent capacitor with a maximum capacitance inμF of no more than at least 10 times the desired descent velocity infeet per minute.

Referring generally now to FIGS. 18-24, the suspension work platformhoist system (10) may further include a tilt control system (1000). Inone embodiment, the tilt control system (1000) is configured so that thework platform (100) reaches and maintains a substantially horizontalorientation as the work platform (100) is raised and lowered. In analternative embodiment, the tilt control system (1000) allows the workplatform (100) to reach and maintain a user specified tilt anglesetpoint as the work platform (100) is raised and lowered. For example,the tilt angle setpoint may be set at a 0° tilt angle so that the workplatform (100) maintains a substantially horizontal orientation when thework platform (100) is raised and lowered, or the tilt angle setpointmay be set at a non-zero tilt angle so that the work platform (100)maintains the non-zero tilt angle when the work platform (100) is raisedand lowered, as illustrated in FIG. 17. It should be noted that the tiltcontrol system (1000) may be incorporated into any of the previouslydiscussed embodiments of the suspension work platform hoist system (10).

With reference now to FIG. 18, the tilt control system (1000) includesat least one tilt controller (1100) and at least one tilt sensor (1200).The at least one tilt controller (1100) may comprise virtually anydevice capable of logic control, including, but not limited to, aprogrammable logic controller (PLC), a programmable logic device (PLD),a complex programmable logic device (CPLD), a field-programmable gatearray (FPGA), DSP, microprocessor, and combinations thereof, just toname a few. In a particular embodiment, the at least one tilt controller(1100) comprises at least one FPGA. The at least one tilt controller(1100) may be programmed with a tilt control algorithm that generates acontrol signal based upon various input signals.

The at least one tilt sensor (1200) may comprise any device capable ofdetecting angular orientation or acceleration forces, including, but notlimited to, electrolytic tilt sensors, magnetic tilt sensors,inclinometers, gyroscopes, accelerometers, and combinations thereof,just to name a few. In one embodiment, the at least one tilt sensor(1200) comprises at least one micro electro-mechanical systems (MEMS)based accelerometer. The at least one MEMS-based accelerometer may be asingle-axis accelerometer, a multi-axis accelerometer, and combinationsthereof, and may have either analog outputs or digital outputs.

The tilt control system (1000) may be in direct electrical communicationwith the constant frequency input power source (800). Alternatively, insome embodiments, the tilt control system (1000) may receive powerindirectly from the constant frequency input power source (800) throughthe variable acceleration motor control system (600) or the platformcontrol system (700), each of which may be in direct electricalcommunication with the constant frequency input power source (800) andthe tilt control system (1000).

As seen in FIG. 18, the at least one tilt controller (1100) is inelectrical communication with the variable acceleration motor controlsystem (600) and the at least one tilt sensor (1200). As previouslymentioned, the at least one tilt sensor (1200) may have either analogoutputs or digital outputs that interface with the at least one tiltcontroller (1100). In one embodiment, the at least one tilt controller(1100) includes outputs that interface with the variable accelerationmotor control system (600) via RS-485 communication lines.

The operation of the tilt control system (1000) will now be discussed inrelation to FIG. 17. As seen in FIG. 17, the work platform (100) hasdeviated from the horizontal, with the dextral end (120) positionedhigher than the sinistral end (110). The tilt control system (1000) iscapable of detecting the tilt angle and controlling the variableacceleration motor control system (600) so that the work platform (100)reaches and maintains a tilt angle setpoint as the work platform (100)is raised and lowered. For example, the at least one tilt sensor (1200)will sense the tilt angle of the work platform (100) and generate a workplatform tilt signal that corresponds to the sensed tilt angle. Next,the work platform tilt signal is received by the at least one tiltcontroller (1100). As mentioned above, the at least one tilt controller(1100) is programmed with a tilt control algorithm that utilizes thework platform tilt signal to generate a speed control signal. Finally,the variable acceleration motor control system (600) receives the speedcontrol signal and controls the operation of the sinistral motor (210)and the dextral motor (310) accordingly to reach and maintain the tiltangle setpoint as the work platform (100) is raised and lowered.

Once again considering FIG. 17, and assuming that the tilt anglesetpoint is set at a 0° tilt angle, the tilt control system (1000) willcommunicate with the variable acceleration motor control system (600) sothat the work platform (100) reaches and maintains a 0° tilt angle. Forexample, in FIG. 17 the work platform (100) is in a tilted state withthe dextral end (120) positioned higher than the sinistral end (110).The tilt control system (1000) will recognize the deviation from thedesired 0° tilt angle and will generate appropriate speed controlsignals that are transmitted to and received by the variableacceleration motor control system (600). For example, the at least onetilt controller (1100) may generate a speed control signal thatinstructs the variable acceleration motor control system (600) toincrease the speed of the sinistral motor (210) to allow the workplatform (100) to reach a 0° tilt angle as the work platform (100) isbeing raised or lowered. Alternatively, the at least one tilt controller(1100) may generate a speed control signal that instructs the variablemotor control system (600) to decrease the speed of the dextral motor(310) to allow the work platform (100) to reach a 0° tilt angle as thework platform (100) is being raised or lowered. Even further, the atleast one tilt controller (1100) may generate a speed control signalthat instructs the variable motor control system (600) to increase thespeed of the sinistral motor (210) and to decrease the speed of thedextral motor (310) to allow the work platform (100) to reach a 0° tiltangle as the work platform (100) is being raised or lowered. In essence,the tilt control system (1000) acts as a feedback control loop thatcontinuously monitors the work platform (100) tilt angle andcontinuously communicates speed control signals to the variableacceleration motor control system (600) to control the operation of thesinistral motor (210) and the dextral motor (310) to reach and maintainthe tilt angle setpoint.

Referring now to FIG. 19, and as discussed above, the variableacceleration motor control system (600) may include a sinistral variablefrequency drive (620) and a dextral variable frequency drive (630). Thesinistral variable frequency drive (620) converts the constant frequencyinput power source to a sinistral variable frequency power supply (910)in electrical communication with the sinistral motor (210), while thedextral variable frequency drive (630) converts the constant frequencyinput power source to a dextral variable frequency power supply (920) inelectrical communication with the dextral motor (310). In thisparticular embodiment, the at least one tilt controller (1100) is inelectrical communication with the sinistral variable frequency drive(620) and the dextral variable frequency drive (630). The sinistralvariable frequency drive (620) receives the speed control signalgenerated by the at least one tilt controller (1100) and controls theoperation of the sinistral motor (210) accordingly. Similarly, thedextral variable frequency drive (630) receives the speed control signalgenerated by the at least one tilt controller (1100) and controls theoperation of the dextral motor (310) accordingly. As a result, theoperation of the sinistral and dextral motors (210, 310) is controlledso that the work platform (100) maintains the tilt angle setpoint whenraised and lowered.

As previously described, the sinistral variable frequency drive (620)may be housed within the sinistral hoist (200), and the dextral variablefrequency drive (630) may be housed within the dextral hoist (300). Inone embodiment, the at least one tilt controller (1100) and the at leastone tilt sensor (1200) are housed within one of the sinistral hoist(200) or the dextral hoist (300). For example, and as seen in FIG. 20,the at least one tilt controller (1100) and the at least one tilt sensor(1200) are housed within the dextral hoist (300). However, it is notedthat the at least one tilt controller (1100) remains in electricalcommunication with the sinistral and dextral variable frequency drives(620, 630). In this specific embodiment, the dextral hoist (300) can bethought of as a master hoist that issues control instructions to a slavehoist, which in this case would be the sinistral hoist (200).

Taking the previous embodiment a step further, and referring now to FIG.21, the tilt control system (1000) may include a sinistral tiltcontroller (1120), a dextral tilt controller (1130), a sinistral tiltsensor (1220), and a dextral tilt sensor (1230). In this particularembodiment, the sinistral tilt controller (1120) and the sinistral tiltsensor (1220) are housed within the sinistral hoist (200), while thedextral tilt controller (1130) and the dextral tilt sensor (1230) arehoused within the dextral hoist (300). As seen in FIG. 21, the sinistraltilt controller (1120) is in electrical communication with the sinistralvariable frequency drive (620), the dextral variable frequency drive(630), and the sinistral tilt sensor (1220). Similarly, the dextral tiltcontroller (1130) is in electrical communication with the sinistralvariable frequency drive (620), the dextral variable frequency drive(630), and the dextral tilt sensor (1230). In this particularembodiment, the sinistral hoist (200) and the dextral hoist (300) eachhave the ability to serve as a master hoist that issues controlinstructions to the slave hoist.

In yet a further embodiment, as seen in FIG. 22, the sinstral tiltcontroller (1120) may additionally be in electrical communication withthe dextral tilt sensor (1230), and the dextral tilt controller (1130)may additionally be in electrical communication with the sinistral tiltsensor (1220). This particular configuration provides the tilt controlsystem (1000) with redundant tilt sensing capabilities that can controlthe tilt angle of the work platform (100) upon failure of either thesinistral tilt sensor (1220) or the dextral tilt sensor (1230).

The tilt control system (1000) may be configured with various safetyfeatures. For example, in one embodiment, the tilt control system (1000)may include a high-tilt alarm. In this embodiment, the at least one tiltcontroller (1100) will generate a high-tilt alarm signal if the at leastone tilt sensor (1200) senses a tilt angle that is above an alarm limittilt angle. For instance, if the alarm limit tilt angle is set at a 10°tilt angle, the at least one tilt controller (1100) will generate ahigh-tilt alarm signal when the at least one tilt sensor (1200) senses atilt angle above 10°. The high-tilt alarm signal is communicated to thevariable motor acceleration control system (600) and instructs thevariable motor acceleration control system (600) to prevent furtheroperation of the sinistral motor (210) and the dextral motor (310).

In yet a further embodiment, the tilt control system (1000) may includea settling mode. The settling mode includes a settling tilt anglesetpoint, and prevents the work platform (100) from being raised orlowered until the tilt angle of the work platform (100) reaches thesettling tilt angle setpoint. In operation, the at least one tiltcontroller (1100) may generate control signals that instruct thevariable acceleration motor control system (600) to incrementallyoperate the sinistral motor (210) and dextral motor (310) until the workplatform (100) reaches the settling tilt angle setpoint. When the workplatform (100) tilt angle, as sensed by the at least one tilt sensor(1200), reaches the settling tilt angle setpoint, the work platform(100) may be raised or lowered. In many instances, but not all, thesettling tilt angle setpoint may be set at a 0° tilt angle, whichcorresponds to a substantially horizontal orientation. Ensuring that thework platform (100) is substantially level allows for higher safetytrajectories when the work platform (100) is raised or lowered.

As previously mentioned, the work platform hoist system (10) may includea platform control system (700), which is often referred to in theindustry as a central control box (CCB). Generally, the platform controlsystem (700) is in electrical communication with the variableacceleration motor control system (600), the sinistral motor (210), andthe dextral motor (310), and includes a user input device (710) designedto accept instructions to raise or lower the work platform (100). Thetilt control system (1000), as previously discussed, may be incorporatedinto embodiments of the work platform hoist system (10) that include aplatform control system (700). In one particular embodiment, the atleast one tilt controller (1100) and the at least one tilt sensor (1200)may integrated into the platform control system (700), as seen in FIG.23. For example, the at least one tilt controller (1100) and the atleast one tilt sensor (1200) may be connected to the PCB of the platformcontrol system (700).

Referring now to FIG. 24, an additional embodiment of the work platformhoist system (10) including a platform control system (700) is shown. Inthis particular embodiment, the platform control system (700) is indirect electrical communication with a constant frequency input powersource (800) and includes a user input device (710) configured to atleast accept instructions to raise or lower the work platform (100). Asseen in FIG. 24, both the variable acceleration motor control system(600) and the tilt control system (1000) are in electrical communicationwith the platform control system (700). Thus, in this embodiment, theplatform control system (700) distributes power to the variableacceleration motor control system (600) and the tilt control system(1000).

Still referring to FIG. 24, the variable acceleration motor controlsystem (600) is in electrical communication with the sinistral motor(210) and the dextral motor (310), and the tilt control system (1000) isin electrical communication with the variable acceleration motor controlsystem (600). This particular embodiment operates in basically the sameway as the previously discussed embodiments that include a tilt controlsystem (1000). For example, the at least one tilt controller (1100) isin electrical communication with the at least one tilt sensor (1200) andwith the variable acceleration motor control system (600), such as byRS-485 communication lines. In operation, the at least one tilt sensor(1200) senses the tilt angle of the work platform (100) and generates awork platform tilt signal that corresponds to the sensed tilt angle.Next, the work platform tilt signal is received by the at least one tiltcontroller (1100). The at least one tilt controller (1100) will thengenerate a speed control signal based upon the work platform tilt signalreceived from the at least one tilt sensor (1200). Finally, the variableacceleration motor control system (600) receives the speed controlsignal and controls the operation of the sinistral motor (210) and thedextral motor (310) accordingly to reach and maintain the tilt anglesetpoint as the work platform (100) is raised and lowered.

The features and variations discussed above with respect to the variousembodiments of the work platform hoist system (10) may be utilized withthis particular embodiment. For example, the variable acceleration motorcontrol system (600) may include one or more variable frequency drives(610, 620, 630), and a sinistral and dextral variable frequency drive(620, 630) may be housed within the sinistral hoist (200) and thedextral hoist (300), respectively. Additionally, this embodiment mayinclude a sinstral tilt controller (1120) and a sinistral tilt sensor(1220) housed within the sinistral hoist (200), and a dextral tiltcontroller (1130) and a dextral tilt sensor (1230) housed within thedextral hoist (300). Moreover, this particular embodiment may beconfigured such that the at least one tilt controller (1100) and the atleast one tilt sensor (1200) are integrated into the platform controlsystem (700), as discussed above.

An additional feature found in this particular embodiment relates to thesafety of the work platform hoist system (10). As discussed previously,the tilt control system (1000) continuously monitors the work platform(100) tilt angle and continuously communicates speed control signals tothe variable acceleration motor control system (600) to control theoperation of the sinistral motor (210) and the dextral motor (310).However, if communications between the at least one tilt controller(1100) and the variable acceleration motor control system (600) arecompromised, there is a high probability that the work platform (100)would begin to tilt and lead to an unsafe condition. In this particularembodiment, the at least one tilt controller (1100) will generate ahigh-tilt alarm signal if the at least one tilt sensor (1200) senses atilt angle that is above an alarm limit tilt angle. For instance, if thealarm limit tilt angle is set at a 10° tilt angle, the at least one tiltcontroller (1100) will generate a high-tilt alarm signal when the atleast one tilt sensor (1200) senses a tilt angle above 10°. Thehigh-tilt alarm signal is communicated to the platform control system(700), which may generate a visible and/or audible alarm, oralternatively may shut off power to the variable motor accelerationcontrol system (600) to prevent further operation of the sinistral motor(210) and the dextral motor (310).

Yet another embodiment the platform control system (700) includes anintelligent control system for the suspension work platform hoist system(10). The intelligent control system is responsible for issuing speedcommands at least one hoist motor (210) by responding to various userinputs, and supervising the overall ascent or descent of the workplatform (100) in a controlled manner. The intelligent control system isboth a real time controller and sequential controller. In a furtherembodiment, the sequential control functions are handled by aProgrammable Logic Controller (PLC), and real time controls are handledby a dedicated microprocessor or Field Programmable Gate Array (FPGA.)

The intelligent control system includes both analog and digitalelectronic circuitry to provide a fail safe mechanism and logicredundancy for the safe and reliable operation of the suspension workplatform hoist system (10). The analog circuit component includes thesensing of current that is being supplied to the control coils of thevarious contactors that apply power to the at least one motor (210), andthe recloser function is accomplished by digital circuit component thatattempts to open and close the control power supply to the control coilsof said contactors. Such an arrangement discerns whether a fault isvalid or not, when actuating a contactor coil that distributes ACelectrical power to the at least one motor (210). By discerning whethera fault is valid or not, the integrity of a ascent or descent of thework platform (100) can be maintained, particularly in the case where afault is invalid. The ability of the intelligent control system todetermine whether a fault exists when actuating a contactor coil isclassified as a diagnostic function. Additionally, the intelligentcontrol system incorporates the ability to provide a prognosticfunction. The prognostic function deals with the ability of theintelligent control system to determine that a voltage actuation circuiton the suspension work platform hoist system (10) is itself bad, or thata contactor control coil has simply aged. The prognostic function isperformed even when no coil actuation is needed. The realized advantageof this approach is to determine that a fault has occurred (diagnostic),or has a significant probability to occur (prognostic) before ascent ordescent. A schematic of the intelligent control system is provided inFIG. 28.

One advantage of the intelligent control system is that is has theability to recognize if control power has been lost to controlcontactors, and alert the users on the work platform (100) of the lossof control power. By having separate power supplies for the digitalcontrol and the power being supplied to the control coils of the powercontactors supplying power to the at least one hoist motor (210), thedigital controls can operate and communicate when a faulted conditionoccurs at the control coils.

In a suspension work platform hoist system (10) safety and reliabilityare of paramount importance. As seen in the schematic of FIG. 29, theplatform control system (700) will distribute power to at least onehoist motor (210), via contactors that will distribute the incomingelectrical power if their control coils are duly energized. In thisparticular embodiment, 24 Vdc is used to control the contactor controlcoils. In the case that there is a faulted condition in at least one ofnumerous control coils suspension work platform hoist system (10), thenwithout proper recognition of this fault, the control circuits will notknow that power is either inadvertently applied or not applied at all.In one particular embodiment this fault detection system a combinedanalog circuit and digital circuit that is linked to dual ProgrammableLogic Devices (PLD) to insure fault redundancy and logic recognition, asshown in FIG. 28. A differential current sensing amplifier monitors theoutgoing 24 V line, and an analog to digital converter transforms thismeasurement into the digital domain, where it is acquired by one PLD. Asecond PLD is also monitoring the same information. If excessive currentis detected, and both the first PLD and the second PLD concur that thiscondition is true, then the main PLD will disable the primary powersupply supplying 24V. In an even further embodiment, a flyback powersupply may continue to supply current even when the output is shorted,and will continue to supply current until either components fail or thePulse Width Modulation (PWM) action of the power supply is disabled.Thus, in this particular embodiment the intelligent control system (i)can attempt to restart the power supply N number of times, where N isvariable and under the control of the main PLD device, (ii) after said Nattempts at trying to restart the power supply, the main PLD will stopthe attempts and report a failure, and (iii) allow the user to instructthe main PLD to continue enabling the power supply, even in a faultedcondition, to identify the source of the fault and hence allow users onthe platform, or on the ground, advanced diagnostic capability.

In yet further embodiments the suspension work platform hoist system(10) may control the speed, torque, direction, and resulting horsepowerof the sinistral motor (210) and the dextral motor (310). The suspensionwork platform hoist system (10) may include voltage-source inverter(VSI) type or current-source inverter (CSI) type inverters.Additionally, the suspension work platform hoist system (10) mayincorporate silicon control rectifier (SCR) technology, insulated gatebipolar transistors (IGBT), and/or pulse-width-modulation (PWM)technology. Further, the suspension work platform hoist system (10) mayprovide soft-start capability that decreases electrical stresses andline voltage sags associated with full voltage motor starts.

In one embodiment, the variable frequency drives (610, 620, 630) andDC-AC inverter (670) of the suspension work platform hoist system (10)utilize current ratings between 4 kHz and 22 kHz carrier frequency. Evenfurther, the carrier frequency may be automatically reduced as load isincreased. The suspension work platform hoist system (10) may facilitatemanual stop/start, speed control, local/remote status indication, manualor automatic speed control selection, and run/jog selection.Additionally, the suspension work platform hoist system (10) mayincorporate a command center to serve as a means to configure controllerparameters such as Minimum Speed, Maximum Speed, Acceleration andDeceleration times, Volts/Hz ratio, Torque Boost, Slip Compensation,Overfrequency Limit, and Current Limit. The hoists (200, 300) mayinclude an LED or LCD display mounted on the door of the cabinet thatdigitally indicates frequency output, voltage output, current output,motor RPM, input kW, elapsed time, time-stamped fault indication, and/orDC Bus Volts. In one embodiment the suspension work platform hoistsystem (10) includes multiple programmable preset speeds which assign aninitial preset speed upon a user contact closure. Further, suspensionwork platform hoist system (10) may include an isolated electricalfollower capability to enable it to follow a 0-20 mA, 4-20 mA or 0-4,0-8, 0-10 volt DC grounded or ungrounded speed signal. Additionally, thesuspension work platform hoist system (10) may provide isolated 0-10 Vor 4-20 ma output signals for computer controlled feedback signals thatare selectable for speed or current. Additionally, further embodimentsmay include the following protective features: output phase-to-phaseshort circuit condition, total ground fault under any operatingcondition, high input line voltage, low input line voltage, and/or lossof input or output phase. The suspension work platform hoist system (10)may provide variable acceleration and deceleration periods of between0.1 and 999.9 seconds.

The traction mechanisms (220, 320) discussed herein are designed to gripthe respective ropes (400, 500) and may be of the solid sheave type,which are known in the art and are currently available via Sky Climber,Inc. of Delaware, Ohio. Further, the gearboxes (230, 330) are planetaryand worm gear systems designed to reduce the rotational speed of themotors (210, 310) to a usable speed. One with skill in the art willappreciate that other gear systems may be incorporated in the gearboxes(210, 310). Additionally, the power terminals (240, 245, 340, 345)discussed herein can take virtually any form that facilitate theestablishment of electrical communication between the terminal and aconductor. While the disclosure herein refers to two hoists, namely thesinistral hoist (200) and the dextral hoist (300), one with skill in theart will appreciate that the suspension work platform hoist system (10)of the present invention may incorporate a single hoist or more than twohoists. Similarly, while the present description focuses on a singlerope (400, 500) per hoist (200, 300), one with skill in the art willappreciate that the present invention also covers applications thatrequire multiple ropes for each hoist, as is common in Europe.

Each of the housings (250, 350) may include separate compartments forhousing the controls and electronics. Generally, the electroniccomponents used in the system (10) must be maintained within a givenambient temperature range, thus it is convenient to house all suchcomponents in a temperature controlled environment. The temperature ofthe electronics compartment may be maintained using any number ofconventional temperature maintenance methods commonly known by thosewith skill in the art. Alternatively, the compartment may be coated withan altered carbon molecule based coating that serves to maintain thecompartment at a predetermined temperature and reduce radiation.

Numerous alterations, modifications, and variations of the preferredembodiments disclosed herein will be apparent to those skilled in theart and they are all anticipated and contemplated to be within thespirit and scope of the instant invention. For example, althoughspecific embodiments have been described in detail, those with skill inthe art will understand that the preceding embodiments and variationscan be modified to incorporate various types of substitute and oradditional or alternative materials, relative arrangement of elements,and dimensional configurations. Accordingly, even though only fewvariations of the present invention are described herein, it is to beunderstood that the practice of such additional modifications andvariations and the equivalents thereof, are within the spirit and scopeof the invention as defined in the following claims. The correspondingstructures, materials, acts, and equivalents of all means or step plusfunction elements in the claims below are intended to include anystructure, material, or acts for performing the functions in combinationwith other claimed elements as specifically claimed.

We claim:
 1. A motor control system for controlling the operation of amotor (210), the motor control system powered by a constant frequencyinput power source (800) via a conductor system (810), comprising: areactive power reducing input power system (1300) in electricalcommunication with the motor (210) and the constant frequency inputpower source (800), via the conductor system (810); wherein the reactivepower reducing input power system (1300) includes an AC-DC converter(640) and a regulator system (650), wherein the regulator system (650)is in electrical communication with a DC-AC inverter (670) in electricalcommunication with the motor (210); and wherein the reactive powerreducing input power system (1300) accepts at least two differentalternating current voltage power inputs including a first alternatingcurrent voltage and a second alternating current voltage, and theregulator system (650) produces a single direct current voltage fromeither the first alternating current voltage or the second alternatingcurrent voltage, and transmits the direct current voltage to the DC-ACinverter (670).
 2. The motor control system of claim 1, furtherincluding an isolation system (680) to electrically isolate the DC-ACinverter (270) from the motor (210) when the DC-AC inverter (270) is nottransmitting power to the motor (210).
 3. The motor control system ofclaim 1, wherein the first alternating current voltage is at least 50%greater than the second alternating current voltage.
 4. The motorcontrol system of claim 1, wherein the first alternating current voltageis at least twice the second alternating current voltage.
 5. The motorcontrol system of claim 1, wherein the first alternating current voltageis a three phase voltage and the second alternating current voltage is asingle phase voltage.
 6. The motor control system of claim 5, furtherincluding a multiple input power connection system (1400) including atleast one single phase power connector (1410) and at least one threephase power connector (1420).
 7. The motor control system of claim 1,wherein the regulator system (650) includes a buck regulator topologygenerating the direct current voltage supplied to the DC-AC inverter(670).
 8. The motor control system of claim 7, wherein the buckregulator topology includes a toroidal stack having an inductance of atleast 2 millihenry.
 9. The motor control system of claim 1, wherein thereactive power reducing input power system (1300) accepts a single phasevoltage, and the regulator system (650) includes a boost regulatortopology generating the direct current voltage supplied to the DC-ACinverter (670), wherein the boost regulator has an inductance of atleast 3 millihenry.
 10. A motor control system for controlling theoperation of a motor (210), the motor control system powered by aconstant frequency input power source (800) via a conductor system(810), comprising: a reactive power reducing input power system (1300)in electrical communication with the motor (210) and the constantfrequency input power source (800), via the conductor system (810),wherein the reactive power reducing input power system (1300) includesan AC-DC converter (640) and a regulator system (650), wherein theregulator system (650) is in electrical communication with a DC-ACinverter (670) in electrical communication with the motor (210); and anisolation system (680) to electrically isolate the DC-AC inverter (270)from the motor (210) when the DC-AC inverter (270) is not transmittingpower to the motor (210); wherein the reactive power reducing inputpower system (1300) accepts a single phase voltage, and the regulatorsystem (650) includes a boost regulator topology generating the directcurrent voltage supplied to the DC-AC inverter (670), wherein the boostregulator has an inductance of at least 3 millihenry.
 11. The motorcontrol system of claim 10, wherein the reactive power reducing inputpower system (1300) accepts a first alternating current voltage and asecond alternating current voltage, and the regulator system (650)produces a single direct current voltage from either the firstalternating current voltage or the second alternating current voltage,and transmits the direct current voltage to the DC-AC inverter (670).12. The motor control system of claim 11, wherein the first alternatingcurrent voltage is at least 50% greater than the second alternatingcurrent voltage.
 13. The motor control system of claim 11, wherein thefirst alternating current voltage is at least twice the secondalternating current voltage.
 14. The motor control system of claim 11,wherein the first alternating current voltage is a three phase voltageand the second alternating current voltage is a single phase voltage.15. The motor control system of claim 14, further including a multipleinput power connection system (1400) including at least one single phasepower connector (1410) and at least one three phase power connector(1420).
 16. The motor control system of claim 10, wherein the regulatorsystem (650) includes a buck regulator topology generating the directcurrent voltage supplied to the DC-AC inverter (670).
 17. The motorcontrol system of claim 16, wherein the buck regulator topology includesa toroidal stack having an inductance of at least 2 millihenry.
 18. Themotor control system of claim 1, wherein the reactive power reducinginput power system (1300) produces a power loss in the conductor system(810) is less than 0.3 W per linear foot of length of the conductorsystem (810) from the constant frequency input power source (800). 19.The motor control system of claim 10, wherein the reactive powerreducing input power system (1300) produces a power loss in theconductor system (810) is less than 0.3 W per linear foot of length ofthe conductor system (810) from the constant frequency input powersource (800).